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Why pinholes occur in the construction of refractory spray coatings

Refractory spray coatings use clay clinker as a raw material. In the coating process, sometimes we find that there are many small pinhole-shaped holes in the coating. What are the reasons for these problems? Here are some reasons why pinholes can occur during construction:
First, the pinhole phenomenon of coating film:
1. It refers to a kind of hollow pinpoint pores appearing on the surface of the paint film, and then the bubbles burst or are broken during the grinding of the paint film to form dense holes like pinholes. Like acupuncture holes, the pore size is about 100 μm.
2. There is gas in the coating that breaks through the coating to form bubbles, and then breaks or wears out to form pinholes. When the dry speed of the surface layer of the coating is slightly higher than the interior, when the surface layer has started to condense and the internal solvent or air continues to evaporate, it will break through the coating surface layer and form bubbles.
Second, the reason for this phenomenon
1. The viscosity of the coating is too high. If the coating is thick at one time, the hole filling does not contain air.
2. The spraying air pressure is too high, and too much air is mixed into the coating.
3. Oil, dust, sweat, etc. are attached to the surface being coated, and moisture is gathered around these unclean objects.
4. The temperature difference between the coating and the surface being coated is too large.
5. Improper use of release agent, excessive addition of curing agent or wrong curing agent.
6, painting environment temperature is too high or relative humidity is too high.
7. When the coating is heated and dried, the temperature is too high, the standing time before the coating is heated is not enough, the solvent is not fully evaporated, the coating itself brings in air bubbles, and the air bubbles generated during stirring have not been eliminated.
Refractory spray coatings will be mixed with a variety of fine powder additives. Cement is a bulk material made of a binder. During the coating process, pinholes appear. It may be because of uneven mixing or insufficient strength or other The reason is also introduced to the above, we only need to control this aspect.
Editor: mxy